1. Field of the Invention
The present invention relates to an article feeding apparatus for feeding articles (various electronic parts such as semiconductor chips) being fabricated to a next manufacturing process or feeding completed articles to a next assembling process.
2. Description of the Related Art
Generally, production lines for articles (various electronic parts such as semiconductor chips) often employ containers in the form of upwardly open boxes for feeding a number of articles to a next fabrication process or a storage chamber.
For feeding a number of electronic parts (hereinafter also referred to as xe2x80x9cworkpiecesxe2x80x9d) with a container along a production line, the workpieces are randomly placed into the container, and the container is automatically delivered to a next fabrication process or a storage chamber by a belt conveyor or a feed arm.
If articles to be fed are small-size articles such as electronic parts, then it is known to employ a feed path having a number of small holes and ejecting air through these holes to feed the articles.
According to the air-feeding process, a number of small-size articles can smoothly be fed to a destination within a reduced period of time while reducing foreign matter which would otherwise tend to be attached to the articles.
The air-feeding process is carried out by a feeding apparatus which is usually made of a metal such as aluminum or steel to meet robustness requirements of the feeding apparatus. However, it is not easy to form small airejection holes in the metal panel of the feed path for controlling a floated state of small articles to be fed. When the feeding apparatus is used for a long period of time, the feed path, which is in the form of a groove, tends to be worn, and particles abraded off the feed path are liable as foreign matter to the articles being fed.
It is therefore an object of the present invention to provide an article feeding apparatus which has an automatized feed system for floating and feeding articles of small dimensions in one direction with air, and which can handle articles in a clean state without producing foreign matter such as small dust particles.
According to the present invention, there is provided an apparatus for floating articles with ejected air and feeding the floated articles, comprising at least one feed path for feeding articles therealong in a feed direction, the feed path comprising a groove, a first layer having side walls of the groove, a second layer serving as a bottom wall of the groove and having a plurality of air ejection holes defined therein, a third layer having an air distribution passage for distributing air to the air ejection holes, and a fourth layer serving as a bottom surface of the air distribution passage, at least the second layer being made of a ceramic material. The ceramic material should preferably be, but not necessarily limited to, partially stabilized zirconia for its strength. The apparatus serves as a feed system for floating articles with ejected air and feeding the floated articles, and lends itself to being automatized.
Since the ceramic material can easily be shaped highly accurately when formed, a plurality of small fluid ejection holes each having a diameter ranging from several tens to several hundreds xcexcm can be defined in the second layer for floating and feeding articles of small dimensions. It is preferable to provide at least three fluid ejection holes per feed area corresponding to one article.
If the first layer having side walls of the groove is made of a ceramic material, then it can be shaped accurately to small dimensions. For example, if semiconductor chips each of a square shape having a size of about 0.2 mmxc3x970.2 mm is to be fed, then grooves as feed paths can be defined in the first layer at a small pitch of about 0.5 mm. The article feeding apparatus may be small in size. If an insulative ceramic material is used, then electrodes may easily be formed on the layers by printing or the like.
All the layers including the third and fourth layers may be formed of a ceramic material. For example, if all the layers are formed and sintered separately and then bonded into a unitary assembly, then the unitary assembly is free of problems such as of warpage or the like due to thermal expansion and shrinkage which would otherwise occur if the layers are made of different materials. Alternatively, formed sheets of the layers may be laminated together and then sintered. This latter process is preferable because no bonding process is required and the layers can be manufactured inexpensively and handled cleanly.
In the article feeding apparatus, furthermore, the first layer may preferably be made of glass or synthetic resin. If electrodes of a metal material are formed on the surface of the second layer which has been formed and sintered, the first layer to be placed on the second layer and then sintered needs to be sintered at a temperature lower than the melting point of the second layer if the second layer is made of a ceramic material. In view of this limitation, it is preferable to make the first layer of glass or synthetic resin which has a low melting point, and to print or coat a sheet of the first layer on the second layer on which electrodes have been printed, and then sinter the sheet of the first layer. Making the first layer of glass is preferable because it is resistant to wear. The application of a sheet of the first layer to the second layer is not limited to the printing or coating process, but may be carried out by bonding a formed sheet of glass or synthetic resin to the second layer with an adhesive. The glass or synthetic resin is not limited to any particular type.
The article feeding apparatus also has a stopper mechanism a stopper mechanism positioned at a terminal end of the feed path, for temporarily stopping an article fed along the feed path, the stopper mechanism having at least a pair of piezoelectric bodies. The piezoelectric bodies have upper ends held at a height slightly lower than the height to which the articles are floated. When a voltage is applied to the first piezoelectric body, it is deformed to lift its upper end to such a height that the first piezoelectric body becomes a barrier in the feed path. An article (first article) which has been fed hits the barrier and is temporarily stopped. Thereafter, the applied voltage is removed to allow the stopped article to be fed to a downstream unloading position at the terminal end of the feed path where the article will be unloaded. The second piezoelectric body is positioned upstream of the first piezoelectric body, and temporarily stops a next article (second article) positioned behind (upstream of) the first article. One or more second piezoelectric body may further be provided upstream.
In conventional apparatus for feeding articles with air, since air is ejected to feed the articles in one direction with no control effected on the articles being fed, articles tend to be held closely against each other at the terminal end of the feed path and hence cannot easily be unloaded. Therefore, it has been customary to unload semiconductor chips individually manually from the conventional apparatus, and the feed system of the conventional apparatus cannot be fully automatized.
According to the present invention, as described above, a voltage is applied to the first piezoelectric body to reliably stop a first article temporarily, and then removed to allow only the stopped article to be fed to the downstream unloading position. When only the first article is fed downstream to the unloading position, a voltage is applied to the second piezoelectric body positioned upstream of the first piezoelectric body for thereby decelerate and stop the second article, which is thus prevented from being continuously fed into overlapping relation to the first article. Consequently, the first article can easily be unloaded at the unloading position.
The article feeding apparatus further comprises a counter mechanism disposed in the feed path, for counting articles fed along the feed path, the counter mechanism having electrodes for detecting a change in a voltage which is produced by a change in an electrostatic capacitance between the electrodes when an article passes over the electrodes. Count information from the counter mechanism is used to automatize the article feeding apparatus.
Usually, the article feeding apparatus has as many grooves as the number of quality levels of articles to be fed, for use as feed paths. If these feed paths are associated with respective article unloading units, then suitable counter mechanisms may be combined with the respective article unloading units. However, facility cost and installation space considerations have prevented the feed paths from being associated with respective article unloading units, but have actually allowed the feed paths to share one or few article unloading units. Accordingly, articles belonging to the respective quality levels cannot individually be counted. According to the present invention, however, a voltage is continuously applied between the electrodes of the counter mechanism, and the electrostatic capacity between the electrodes varies depending on whether an article passes over the electrodes or not. Such a variation of the electrostatic capacity is detected as a voltage change. Since the electrodes can easily be provided in each of the feed paths, articles belonging to the respective quality levels can individually be counted with ease. If the counter mechanism is positioned at an intermediate position in each of the feed paths, then the counter mechanism may be used as a sensor for detecting when a certain number of articles remain stagnant between the unloading position and the intermediate position.
While being fed along the feed path, the preceding first article is constantly pushed by and held against the following second article, and hence these articles cannot reliably be distinguished by the counter mechanism. Therefore, the counter mechanism is placed in the unloading position at the terminal end of the feed path where the preceding first article is reliably separated from the following second article. The counter mechanism thus positioned is effective in counting articles fed along the feed path, without fail.
The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example.